When firearms are shot the barrel and its other parts experience various degrees of wear and tear. In the case of semi-automatic or automatic firearms (such as the SigSauer 556 or Colt M41A automatic rifles), each firing cycle results in the expansion of the chamber by the hot corrosive gases, the acceleration of the bullet down the barrel, and an ejection of the spent case and re-loading of a new cartridge for the next firing cycle. This cycle may be repeated in different rates such as single shots, burst fire (e.g. 3 shots in rapid succession) and full automatic fire. All of the weapons parts wear, including those in the gun's action and barrel such as the hammer, firing pin, and the bolt, as well as the chamber, gas ports/vents, barrel, and the various springs, screws, and washers in a gun that control the magazine, control recoil, control gases, and control movement of bullets into the chamber.
The parts become progressively worn until they are no longer serviceable and must be repaired or replaced. In many cases the wear status of these parts and overall usefulness (accuracy) and safety of the firearm is directly proportional to the number of shots that have been fired. Therefore, routine maintenance on a firearm is critical, especially for professionals who depend on the accuracy and reliability of the weapon, such as those in the military and law enforcement disciplines. Unfortunately, the need for routine maintenance is typically calculated by the shooter's memory of the type (rapid fire versus single shot), firing cadence and the total number of shots fired since the prior maintenance.
This is not accurate because humans can fail to remember the exact total number of shots fired or the proportion of those shots fired at a specific rate of fire (also known as cadence), especially in war or other hostile situations. For example, a manufacture may recommend that routine maintenance be performed (for example, changing the springs) after 3,000 rounds. Or, after 10,000 rounds the barrel should be replaced, and so on. In many other weapons the wear and tear may be accelerated depending upon how close the rounds were fired together. This is especially true in automatic and semi-automatic weapons that can fire up to 13-15 rounds per second. At this rate the heat generated from bullets can have a harmful affect on the barrel and other moving parts, especially if it is a sustained action. For example, if a specific firearm (automatic or semi-automatic type) has a total of 3,000 rounds fired over its lifetime, the rate of fire for these past firings has a profound effect on the maintenance required by the firearm. For a specific type and model of firearm, a firing rate of one shot per second for 3,000 rounds may be acceptable for maximum barrel life, bolt life, spring life and overall maximum lifespan of the weapon. However, if the same 3,000 rounds are shot at much higher rates of fire such as ten rounds per second, the accelerated wear may make the weapon inaccurate, or unusable and unsafe.
For more background on the effect of shot cadence and accuracy, reliability, and safety for military firearms, refer to the public document “SOPMOD Program Overview” published by the NSWC of the US Navy on April, 2006.
Therefore a system that monitors shots and shot timing is necessary for these weapons.